text:
What has happened to make me experience negative G with the control stick FULL AFT near the top of a loop?
I experienced negative G with the control stick FULL AFT near the top of a loop.
My questions:

Aerodynamically, what happened? Was the wing meeting the air at a negative-lift angle-of-attack (creating a skyward lift force) at this instant?
How can I change my technique to prevent this?

Welcome to Stack Exchange. This isn't usually a good place to ask "survey" questions or questions about other people's personal experiences; this site is designed for questions that have a particular "right answer". Consider editing your question so that it doesn't mention "you".

Are you looping a glider?

This question is confusing. By "negative G" can we assume you are referring to the apparent force wrt the aircraft? If you don't have enough speed at the top of the loop your apparent g-force will go negative regardless of what direction the lift force is. So it's a little unclear what you're looking for

@TomMcW But the apparent g-force is the lift force, isn't it? The proper acceleration that the occupants feel is always proportional to the non-gravitational forces exerted on the aircraft (and in flight, the only non-gravitational forces are aerodynamic forces). So it's not possible for the apparent g-force to be away from the floor unless the lift force is towards the floor.

@TannerSwett If the plane is upside down the apparent G-force wrt the plane is negative unless you have enough speed to create enough centrifugal force to counter gravity. When I say negative G I'm talking toward the ceiling of the plane. I'm not exactly sure if that's what the op means

@TomMcW, no, Tanner Swett is right—apparent G-force equals sum of aerodynamic forces (of which lift is dominiant), always.

@JanHudec The sum of aerodynamic forces.and gravity.

@TomMcW, No, just the aerodynamic forces (with opposite sign). In straight and level normal side up flight, the lift equals gravity and apparent G-force is one G. So equal to lift, not the sum of lift and gravity, which is zero in that case (as they have opposite signs).

@JanHudec I see what you're saying. But if the plane loses speed and there's just no lift at all, and you're upside down then you - and the plane - will start falling. So I guess you would experience zero g. But I would expect the plane would have more resistance to falling, not necessarily lift but I guess it would be drag, just not from the usual direction

@TomMcW, yes, if the angle of attack approaches 90° (falling flat), then the dominating aerodynamic force will be drag. But as long as the loop you attempt looks at least a bit as a loop, there is always at least a bit of positive lift and positive G-force. Only when the attempted loop turns into something else will you experience G-force in other directions (in a hammerhead it will be zero and then a bit sideways as you turn over the wing, in a tail slide it will be backward as you descend tail down).

Please [edit] this question - I think there's a good question in here, it just needs to be phrased differently.

If you are experiencing negative G at the top of a loop with the stick full aft it is definitely no longer a loop.  And @JanHudec is correct, the apparent G is the sum of the aerodynamic forces plus gravity.  In the fighter world they compare the effect to an egg, where the pointy end of the egg is up.  For a given apparent G your turn rate will be much tighter at the top of the egg because gravity is helping you, whereas at the bottom gravity is working against you.

I'm also curious about the rationale for putting this on hold:  While maybe not the best question, it certainly appears to be about aviation and has spurred some interesting discussion.

This site is for questions and answers about aviation, not about individual people. "Has this happened to you" is a question about individual people. "Is it possible for this to happen" and "How can I prevent this from happening" are questions about aviation. That's why this question needs to be improved, in my opinion.

@DanPichelman FYI, we tend to prefer titles to be in question form around here.

I've rephrased the question to hopefully make it more on topic.  There are rules about how much editing is acceptable, and this may have crossed that line.  You can always [edit] or roll back the changes if need be.

@Federico - better?  I'm a little concerned about this edit.  I hope I didn't cross the line.

@DanPichelman If OP is fine with it, you not have crossed any line, and OP can always edit back. Title is still not ideal imho. Going to edit it myself.

@Federico - works for me.

OK with the edit. I agree with the people who are saying that gravity and/or "centrifugal force" don't contribute to force "felt" by the pilot (and by the aircraft structure.) Only aerodynamic forces do. I think the wing's angle-of-attack was negative due to the tight radius of curvature of the flight path (gravity DOES contribute to this) causing the relative wind to be highly curved.  Due to the curving flow, unless the fuselage were able to bend like a banana, full aft elevator is unable to command a positive AOA at the wing.  Faster entry speed=larger radius of loop and avoids issue.

PS a requirement for a high rate of pitch rotation, and the resultant"pitch damping" effect, is another way to think of the situation.  Pitch damping and curving relative wind are two sides of the same coin.

PPS all the above is one reason why an all-moving horizontal stabilizer can be a good thing.  Fully all-moving stabs may be poor in terms of giving a nice increase in stick force with G-loading but look at the tail of this Fox aerobatic glider--  https://media-cdn.tripadvisor.com/media/photo-s/04/2c/b4/e2/boonah-gliding-club.jpg -- the elevator comprises more than half the total horizontal tail area.  PPPS yes I have looped gliders-- great fun.

@JanHudec: Now you have disappointed me - for the first time! TomMcW is right and Tanner is wrong. Of course there is more than just gravity and aerodynamics when the airplane is on a curved path.

@quietflyer: The Swift elevator is sized for sufficient control forces. Has very little to do with effectivity - a smaller one would work equally well but gives the pilot less response. And I have looped not only a number of gliders, but the Swift prototype, too.

@Peter Are you saying that in flight, the vector of proper acceleration felt by the occupants isn't proportional to the vector of aerodynamic force on the aircraft? If that's what you're saying, I'll post a question in order to resolve the matter.

@TannerSwett: Well, the inertial forces acting on the plane and on the occupant are the same, but they are still there, even if you have the sensation of them being absent because both of you move the same way. But besides aerodynamics there is also thrust to consider. And when moving at slow speed, aerodynamics forces become low.

Re whether inertial forces need to be considered-- see this answer to related question "What is the definition of load factor & how do you apply it?" https://aviation.stackexchange.com/questions/46287/what-is-the-definition-of-load-factor-how-do-you-apply-it/56634#56634

You were too slow.
Start the loop with more speed and pull more (if the g limit of your aircraft allows) at the beginning, so you have more speed at the top.

Aerodynamically, what happened?

Without aerodynamics, you feel -1 g at the top of the loop, simply by having inverted the plane. Since the plane feels the same acceleration, both of you move together - until vertical speed picks up and drag will keep the airplane back. This is when you have the sensation of negative gs. In order to stay with positive gs, you need a centrifugal force to compensate for earth's gravity. This is the product of pitch rotation speed squared and the radius of the loop. If your flight speed drops, the radius will drop as well and leave little centrifugal force, even at a high rate of pitch. Dan Pichelman correctly describes how this kind of loop looks to an outside observer.
So there is little aerodynamics involved here besides drag - low speed will reduce all aerodynamic forces. The angle of attack on the wing is insignificant - what counts is the inertial force of the moving aircraft (besides gravity, of course).
If your airplane places you behind the center of gravity, pulling hard will give you the sensation of negative gs even when the aircraft as a whole is still at positive gs. Any maneuvering will add inertial effects which grow with the pilot's distance from the center of gravity.

How can I change my technique to prevent this?

Fly faster, and be fast enough at the top to push in order to round out the loop, so it will look more like a circle. But make sure to stay within the limits of your plane. Again, Dan is right: It really sucks when the wings fold up.
Negative gs are completely normal at the top of the loop. When I did my first loop in an open-cockpit aircraft (a Boeing Stearman, no less), I did exactly that: Push near the top. However, this did not last long because my instructor immediately whined "pull, pull!". He had not closed the pockets of his flight jacket and started to lose their contents. So make sure that all equipment is secured before doing aerobatics.

Did you read and consider all the comments posted under the question, especially those by Tanner Swett, especially "But the apparent g-force is the lift force, isn't it? The proper acceleration that the occupants feel is always proportional to the non-gravitational forces exerted on the aircraft (and in flight, the only non-gravitational forces are aerodynamic forces). So it's not possible for the apparent g-force to be away from the floor unless the lift force is towards the floor." I agree w/ him.  You don't "feel" gravity in flight, and centripetal(or inertial)  force is only a pseudoforce.

@quietflyer: The aircraft experiences more than only aerodynamic forces. When moving other than straight, inertial forces will become important. Just because it is typed in a comment does not make a statement correct. Regarding "pseudo forces": There is a lot of nonsense out there on those forces. When your system of reference is moving, they become very real indeed. Regarding gravity: Of course you feel it all the time! What else keeps you in your seat in level flight?

@PeterKampf-- Well, it's hard to disagree with someone with 152k reputation points and flight experiences such as you speak of-- yet I'm afraid I do.  It is not invalid to chose a reference frame such as you speak of (the aircraft) but it is also not invalid to choose a true inertial reference frame.  The current version of my answer says a bit more on this so I'll avoid saying a lot more in the comments.

@quietflyer: As long as you are strapped to that airplane, using its frame of reference simplifies things.

Re comment above -- what happens the atmosphere goes away and you are suddenly in a vaccuum?  Does the G-force instantly go to zero (except for apparent G-load due to rotation about aircraft's CF IF pilot is not seated at CG -- or does it not?  In other words is the G-load essentially just a reflection of aerodynamic load, or is it not?  The answer is more obvious if you are using the earth (or the linearly moving airmass) as a reference frame, not the aircraft.

Re latest edit-- in most cases surely the apparent G-load created by the rotation about the aircraft's CG-- as opposed to the apparent G-load created by the rotation about the center of the loop, which is just a reflection of the net aerodynamic lift force-- is very small.  Because the pilot of an aerobatic aircraft is usually seated rather near the CG.  An exception would be something like say an F-8 Crusader.  In my case I was seated in front of the CG, not behind it, so the rotation about the CG could not have contributed negatively to the total felt G-load.  The aircraft was a sailplane.

Let's look at the question. The pilot FELT negative G.  This would be Gs generated by the plane upward MINUS gravity.  The plane is too slow or not tight enough.  Speed up more Gfelt = Gaerodynamic - Ggravity goes to weightless or positive.  Throttle modulation might help here.  Again, if the plane can handle it, one might enter loop at V abrupt, go to vertical, firewall the throttle, and reduce after going over the top.

@RobertDiGiovanni That is how you fly a looping in old aircraft. Slow the engine to idle so you will not overspeed it. Go into a dive in order to speed up. Pull. Add full power on the way up as the plane slows down, but do not forget to go back to idle once the aircraft is over the top. And: You guys all assume the pilot to be in the center of gravity. That is not necessarily true, and adding a pitch rate will add inertial loads, independent of aerodynamics.

I would think that would work in a newer one too ;-).  Interesting, to maintain constant Gfelt in a loop, it might be more egg shaped at constant speed, whereas a perfectly circular one at constant speed would have variable Gfelt.  It would be fun to measure and record Gfelt (as simple as did the coffee spill) and roundness of loop using variable speed.  I still do not know how a 1G barrel roll makes it easier.

Re whether inertial forces need to be considered-- see this answer to related question "What is the definition of load factor & how do you apply it?" https://aviation.stackexchange.com/questions/46287/what-is-the-definition-of-load-factor-how-do-you-apply-it/56634#56634

A typical "for fun" loop flown by someone with little experience is typically shaped like a cursive lower case "L" or "E" rather than a circle.  There's a fairly gentle pull from horizontal to vertical, then a sharper pull at the top.
If that was the case, you could have easily pulled to vertical, let up on the stick pressure to go nearly straight up for a while, then pulled a bit harder to bring the nose over the top.
You'd then be left hanging from your seat belts for a few seconds (more if you didn't keep pulling back on the stick) until the nose pulled through back to level flight.

Aerodynamically, what happened? Was the wing meeting the air at a negative-lift angle-of-attack (creating a skyward lift force) at this instant?

Yes, from the point of view of the wing, you briefly had a negative lift angle of attack.

How can I change my technique to prevent this?

Make sure your plane is rated for aerobatics.  A small mistake can easily exceed ultimate load limits.  It really sucks when the wings fold up.
Go up with a qualified instructor.  Wear parachutes.  If you need to find an instructor, poke around on www.iac.org
Learn where to look:

Look over the nose as long as you can see the horizon.
Look at your left wing tip until you're at the 3/8's point of the loop
Look straight up through your canopy or roof window and catch sight of the horizon

Keep the "rate of pitch change" constant.

Can't emphasize this enough: "Make sure your plane is rated for aerobatics. A small mistake can easily exceed ultimate load limits. It really sucks when the wings fold up."

Yeah, and keep your knots and Gs where they need to be.  I was thinking it wouldn't be possible, (hypothetical question) but if this actually happened you obviously messed up the loop.

@MichaelHall The relationship between Gs experienced and elevator position isn't always as simple as one might think.  That's why if you're low and slow pulling back on the stick might be a bad idea.

Thanks Dan.  I’ve been flying for a few years now and kinda knew that already...  ;)

Gravity and/or "centrifugal force" don't contribute to force "felt" by the pilot (and by the aircraft structure.) Only aerodynamic forces do. Actually the apparent centrifugal force created by the rotation ABOUT THE AIRCRAFT's CG is "felt" by the pilot, but that would appear to contribute a positive G-load component to a pilot sitting in front of the aircraft's CG during a loop.  This would surely only be significant in an aircraft with the cockpit far in front of the CG, rotating very rapidly about the CG.
For negative G to occur near the top of the loop, the wing indeed must have been at a negative angle-of-attack at that point, even with the stick full aft.  Here's how that could happen:
At the top of the loop, the airspeed was quite low, meaning that the flight path had a very tight (small) radius of curvature of the flight path due to the low airspeed.  Note that gravity and aerodynamic force both combine to determine the aircraft's total curvilinear acceleration through space, and gravity is forcing the flight path to curve earthward at the top of the loop, even if the aerodynamic lift force is very small or even negative (skyward).  Since various molecules of the aircraft are moving in different directions at any given instant (think of a flat spin for an extreme example), the relative wind (meaning the undisturbed airflow-- the apparent wind created by the motion of the aircraft-- the direction the airflow would be coming from if not altered by the disturbance created by the physical presence of the aircraft) "felt" by any given point on the aircraft's surface curves to follow the path of the turn.  This means that the actual airflow will also have a curvature to it. If the loop has a very tight radius at the top, this effect will be extremely significant.
Unless the fuselage is able to bend like a banana (with the "canopy" side being the concave side and the "belly" side being the convex side) to conform to the curving flow, we can visualize (loosely speaking) that the curving flow will tend to "push up" against the bottom ("belly" side) of the horizontal tail and pitch the nose toward the aircraft's belly-- toward the sky in this case.  It's as if we're giving the aircraft some negative decalage.  Due to this pitch torque, full aft elevator may be insufficient to command a positive AOA at the wing. A faster entry speed (or stronger initial pull) increases the airspeed over the top of the loop, increasing the radius of the loop and avoiding the issue with negative G.
Another way to think of the "curvature in the relative wind" is to note that a pitch rotation always leads to some amount of "pitch damping" effect. Pitch damping and curving relative wind are two sides of the same coin.  Either way we look at it, we see that the "free-stream" or undisturbed relative wind tends to be directed "up from below" (i.e. has a vertical component aimed from belly toward canopy) at the rear end of the fuselage during a loop, which tends to pitch the nose "down" (toward the belly), decreasing the angle-of-attack of the wing.  The actual airflow over the rear end of the aircraft will be affected by the wing's downwash, but a given nose-up elevator input will still end up creating less nose-"up" pitch torque when the flight path is curving in the nose-"up" direction (toward the canopy), than it would if the flight path were completely linear and the pitch rotation rate were zero.  The curvature of the relative wind--the pitch damping effect-- effectively reduces the elevator's "purchase" or "leverage" on the air and reduces the amount of nose-"up" (towards the canopy) pitch torque created by the raised elevator, compared to what we'd see at the same airspeed if the flight path were linear.  A normal constant-airspeed turn also involves some pitch rotation, so the same effect is present to some degree-- more on this later.
These dynamics are a reason why an all-moving horizontal tail can be a good thing-- especially in radio-controlled model aircraft where stick force is provided by springs in the transmitter and thus the stick-force-per-G characteristics aren't a concern.  Fully all-moving stabs may be poor in terms of giving a nice increase in stick force with G-loading but look at the tail of this Fox aerobatic glider -- the elevator comprises more than half of the total horizontal tail area.  (This is NOT the glider in which I experienced negative G over the top of the loop!)
In my personal experience, if the loop is in the clockwise direction and 12 o'clock is the top of the loop, and the airspeed gets too low over the top of the loop, the negative G (with stick full aft) will occur from about the 12:30 through the 1:30 or 2:00 positions, not at the very top of the loop.  It appears that the point of lowest airspeed does not occur at the point of strongest negative G, and the G-load may in fact have be positive at the point of lowest airspeed, which probably occurs somewhere between the 12:00 and 12:30 positions.  I don't know the reason for this.  Perhaps I was mis-perceiving the aircraft's position in the loop due to the unusual attitude and un-accustomed sight picture, but I don't think so.  Since pitch torque commands a change in rotation rate, rather than directly governing rotation rate, perhaps there was simply a time lag between the time the tail started "feeling" a strong change in the direction of airflow due to the decreased radius at the top of the loop, and the time that the aircraft's pitch rotation rate had been altered enough by this pitch torque, relative to the (not necessarily constant) pitch rotation rate that would have been required at any given instant to hold the angle-of-attack constant, to drive the wing to a negative angle-of-attack.  This is only a hypothesis.
The negative G was very mild, but enough to make objects rise up against the canopy.
My recollection is that the problem was avoided if I did not let the airspeed drop below 40 mph at its lowest point.
The curvature in the relative wind is also present in a normal turn and requires the stick to be further aft to command a given angle-of-attack while turning than in wings-level flight.  Due to the low airspeed involved, this effect is extremely noticeable during a thermalling turn in a sailplane.  I know of at least one sailplane in which the total "up" elevator throw is somewhat limited to help prevent stalls and spins, and heavy pilots (who move the aircraft's CG to near the forward edge of the allowable envelope) find it is not only nearly impossible to stall in a turn (absent a sudden sharp gust from below), but difficult to maintain a slow enough airspeed for optimum thermalling, even with the stick full aft.  They simply don't have enough elevator power to put the wing at the optimum (high) angle-of-attack during a steep thermal turn.  During wings-level linear flight, those same pilots have no problem commanding a stall, or putting the wing at the optimum (high) angle-of-attack required to achieve flight at the lowest possible sink rate.
On a more fundamental level, the reason we don't "feel" gravity is that gravity exerts an equal force per unit mass on every molecule of the aircraft and pilot's body, all at the same time, thus creating no stresses or strains with the body or structure, and creating no tendency for the pilot to move toward or away from the seat of the aircraft.  In flight, we only feel aerodynamic forces.  Examples: 0G flight-- total acceleration-- 1G downward-- felt acceleration -- 0G.  Flying straight and level-- total acceleration--0G-- felt acceleration-- 1G upward lift force (per unit mass) generated by wings. Standing still on solid ground-- total acceleration--0G-- felt acceleration-- 1G upward push force (per unit mass) of floor against soles of feet. In all cases "felt" force + gravitational force = "total" force.
IF we adopt the aircraft as our reference frame, THEN we have an accelerated reference frame and we do have to consider centrifugal (inertial) force.  Also, if we consider the aircraft to be a fixed reference point, then it is valid to say that the pilot will tend to "feel" gravity pulling him against his seat in normal upright flight, and against the seat belts in sustained inverted flight.  At any given instant, the total force that we compute that the pilot will end up "feeling" will come out the same whether we choose the aircraft as a reference frame, which requires us to consider centrifugal (inertial) force and gravity, or we choose a true inertial reference frame, in which case centrifugal (inertial) force vanishes and gravity is a force that creates an acceleration but cannot be "felt".  However in an accelerated reference frame it is no longer true that F=ma, so this is not a good choice of reference frame if we want to discover the fundamental cause of the total force acting on the aircraft, the total acceleration acting on the aircraft, and the G-load "felt" by the aircraft and pilot.
To put it another way-- the apparent centrifugal force created by the rotation about the center of the loop (as opposed to the rotation about the aircraft's CG) is a pseudoforce that is simply equal and opposite to the real, aerodynamic centripetal force generated by the aircraft.  That's all it is.  Whether or not we count it in our calculations depends on whether we are using an accelerated reference frame that is tied to the aircraft, or an inertial reference frame such as the earth or airmass (in the latter case, assuming that any wind present is linear and not a rotating such as a dust devil or rotating thermal column etc.)
To help understand the advantage of choosing a true inertial reference frame such as the earth over an accelerated reference frame such as one moving with the aircraft, consider this question-- at an instant in time where the G-load is negative (with the stick full aft) near the top of the loop as described in the original question, if we suddenly took away the atmosphere so that the plane was in a vacuum, while preserving the same initial velocity and the same gravitational force, would the "felt" G-load-- the G-load on the G-meter-- instantly go to zero?  Why or why not?
Outside links pertaining to the curvature in the relative wind in turning flight (not loops specifically)
"Circling the Holighaus Way" by Richard H. Johnson--A key point is that as a glider circles, if the fuselage is tangent to the curving flow near the CG, then it will not be tangent to the curving flow near the nose--and the yaw string will be slightly deflected to the outside of the turn.  There's a bit more to it than that though.
"Spiral Stability and the Bowl Effect" series-- by Blaine Beron-Rawdon-- pertains to stability and control of rudder-controlled rc sailplanes--

Part 1
Part 2

I appreciate the other answers and the various comments.  I know this really isn't a discussion forum.

as mentioned already under another answer of yours, please avoid: overly long answers, and continuous edits.

Re whether inertial forces need to be considered-- see this answer to related question "What is the definition of load factor & how do you apply it?" https://aviation.stackexchange.com/questions/46287/what-is-the-definition-of-load-factor-how-do-you-apply-it/56634#56634


text:
What happens when auto-pilot fails over the ocean?
Let’s assume the current location puts the aircraft 2 hours from the nearest airport, but the destination is 2 1/2 hours away.
Would the pilots hand fly the rest of the way?
Are they allowed to fly to their destination, although it’s just an additional 30 minutes?
And how difficult would that be (For the sake of the conversation, we can say I’m specifically asking about the 787, but I am generally interested in long distance capable aircraft)? Or is there tons of ways to fix the auto pilot?
In short, what I’m asking is: how difficult it may be for two pilots to manually fly for this long, is it a big enough deal to cut the flight short 30 mins to land elsewhere?
I'm not sure under what rules, and not sure how the auto-pilot fails either.

@PerlDuck In RVSM airspace it is usually not allowed.

@Federico thanks for the edit. So I take it you cannot answer or perhaps being passive aggressive due to my flight attendant remark?

@PerlDuck no problem. I just thought he may have taken it the wrong way.

I don't know enough to provide a precise and factual answer, but I wanted to avoid the question being closed

Think of it this way:  If you were driving on the freeway and your cruise control stopped working, would you stop short of your destination or would you continue?

Are oceanic operations governed by RVSM?  I thought RVSM was a requirement for controlled airspace.  What ruleset defines RVSM while oceanic?

As @Bianfable points out in the comments RVSM airspace is a problem but ignoring that for a minute:
The question of will they continue? depends on the airlines op-specs. Different airlines will handle this differently and it may very well be handled different on different airframes within an airline. A call to base may even occur but there are lots of factors that can play into it such as what other equipment is operable.
Assuming the Op-Specs dictate that the flight continues

how difficult it may be for two pilots to manually fly for this long

Potentially not too difficult at all, most pilots trained in aircraft with no autopilot and all pilots are qualified to hand fly the aircraft. However after Op-Specs it is ultimately up to the pilot and they will consider many factors. Hand flying an aircraft in IMC can be a tiring task for even the best of pilots, a pilot may chose to divert or land sooner if they feel it would be unsafe to continue even if they are capable of flying the aircraft by hand.

They will just fly manually, or if it was hard, they will make an emergency landing.

source: Stack Exchange

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

sort: votes


text:
Is there a good systematic approach to flying an 800 foot pattern?
I have a systematic approach to flying a 1000 foot pattern:  abeam the threshold, start a 500 fpm descent; turn when 300 feet below pattern altitude; etc.
Does anyone have a systematic approach to flying 800 foot patterns?  I'm looking for something more definite than "start a descent, don't get too low, turn on the 45, etc".

It may depend on the environment. The answer may be specific to your airport

The trick of putting the runway half way down your wing strut visually, or a third to a half way down the wing on a low wing works great, because it automatically allows for any altitude agl being flown. As far as the rest of the pattern goes, just fly it with the same power settings and airspeed you would have in a1000 foot pattern. The base leg will get turned maybe a tiny sooner than the usual 45 degrees behind you trick, since you are starting out 200 feet lower (so you don't want to go as far away) I think it's more important that you just fly the pattern no differently...just make sure you're not out wide on downwind. The trick to consistent landings is consistent patterns and approaches. And that only comes from making sure your first circuit around is by the numbers. (i.e. airspeeds and power settings were exactly right and exactly at the proper place when they happened) Adjust accordingly after that first one, but really quiz yourself and make sure you are being consistent in the first place, before you start changing up how you do things.

The reality of traffic pattern work is, that beyond a few basic and generic procedures, the details of flying a traffic pattern are all going to be based upon the aircraft you are flying, the airport that you are at, nearby obstacles or terrain, weather concerns, ad hoc input from ATC, etc.  A traffic pattern in a Cessna 172 at 85 KIAS is going to be quite different from that flown in a T-38 at 270 KIAS, but both use the same basic procedures.
My general approach to a VFR traffic pattern
VFR PATTERN - single engine aircraft

DEPARTURE LEG from 0-400 ft AGL

positive rate of climb, gear up (if equipped)

DEPARTURE LEG greater than 400 ft AGL

flaps up
set Vy and begin climb out.
set prop speed first then climb manifold pressure
clean up; boost pump off, ldg lights off, etc.
begin turn to crosswind leg (square pattern) or downwind leg (round pattern)

DOWNWIND LEG

level out at pattern altitude for field; reduce throttle to set pattern airspeed

THE PERCH (generally abeam threshold "piano keys")

Configure for landing.  Gear and flaps down, prop full, etc. GUMPS check.  Set descent airspeed.
Turn base or final at your discretion and/or as circumstances permit.

FINAL APPROACH

Set approach speed
VERIFY on or above glidepath; aim for the numbers / white-red VASI, etc.
Final check: gear down-locked, three greens.

VFR PATTERN - multi engine aircraft

DEPARTURE LEG from 0-400 ft AGL

positive rate of climb, gear up (if equipped)
accelerate while climbing to Vyse (blue line is lifeline).

DEPARTURE LEG greater than 400 ft AGL

flaps up
set Vyse and begin climb out.
set prop speed first then climb manifold pressure
clean up; boost pump off, ldg lights off, etc.
begin turn to crosswind leg (square pattern) or downwind leg (round pattern)

DOWNWIND LEG

level out at pattern altitude for field; reduce throttle to set pattern airspeed

THE PERCH (generally abeam threshold "piano keys")

Configure for landing. Gear and flaps down, prop full, etc. GUMPS check. Set descent airspeed at Vyse (Blue line is lifeline).
Turn base or final at your discretion and/or as circumstances permit.

FINAL APPROACH

Set final approach speed at Vyse.
VERIFY on or above glidepath; aim for the numbers / white-red VASI, etc.
Final check: gear down-locked, three greens.
Once you are assured you can make the runway at 1.3 Vso at round out, throttles to idle; go-around will be impossible if engine failure occurs below Vmc.  Do not attempt.

AND
IF IT JUST DOESN'T LOOK RIGHT OR THINGS JUST ARENT LINING UP RIGHT - YOU CAN ALWAYS GO AROUND!

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
What does it mean to maintain a positive g loading?
When we hear about a "g", if I am not mistaken, one "g" is an equivalent force to that which is experienced when we are standing at sea level.  So what does it mean if a plane maintains a positive g loading and vice versa when a plane maintains a negative g loading along with how it feels to someone inside.

Google "707 barrel roll"  for what can be done while maintaining 1 g positive loading...

Put something on the top of the instrument panel of a shape that it won't shift from side to side. If it doesn't float off vertically, you are maintaining a positive g loading. Now, making sure your seatbelt is firmly around you, push over until that object floats off the instrument panel. You have now experienced a negative g loading. My kids used to refer to the maneuver as "doing humps."

Short Answer
In straight and level flight, it means don't push over too fast.  Doing so gets you "light in the seat" and things may fly about the cockpit/cabin.  In some aircraft, negative "g" can make the oil "flow up" away from the sump and begin to starve your engine of much needed lubrication. (Example: T-34C, trainer, limited to 10 seconds inverted flight.  Straight and Level inverted flight is -1 "g.")
More Answer
You want to avoid flying with negative "g" in a variety of circumstances,  depending upon how the aircraft is designed.

Example: In a helicopter, negative "g" can have dire consequences.
On the teetering, semi rigid rotor heads in the original Huey, for
example, unloading the head can lead to mast bumping, which can
lead to catastrophic failure of the mast, and then some death.
Counter Example: Flying a Pitts Special, or an F-18, the aircraft is
built to withstand some negative "g" due to their needing to fly
particular maneuvers.

"G" is a natural part of flying, but "how much" varies with design.
Whenever you turn the aircraft, you will add a little bit of "g" load since "g" is a measure of acceleration.  Vector sums based on angle of bank will tell you how much "g" you can expect in a level turn at constant speed.

Example: a 60 degree angle of bank adds an additional "g" compared to
level flight, and you feel a bit of a push into your seat.

An item inside the plane that is not attached will accelerate towards the

floor during positive g
ceiling during negative g

The item will seem to float at zero g.
Note that during inverted flight the floor is up, and the ceiling is down.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
How are military aircraft numbered?
Can someone describe the numbering system used by the military and how it has changed over the years?  I know that there are fighter aircraft such as the F-15, F-16, F-22, etc but why are there aircraft numbered like the F-117?  and why is the B-2 a B-2 when we have had B-17s in the past?

Surely you mean only in the American army?

Related: http://aviation.stackexchange.com/questions/20899/why-isnt-the-f15e-called-f-a15  and http://aviation.stackexchange.com/questions/20920/was-the-intended-purpose-of-the-f-117-nighthawk-originally-a-stealth-fighter?noredirect=1&lq=1

@Antzi None of those aircraft are flown by the American Army.

At present, all US military aircraft follow the 1962 United States Tri-Service aircraft designation system. The first letter ('F' or 'B') denotes the mission of the aircraft, while the number denotes the design number. The designation system produces a Mission-Design-Series (MDS) designation. From Designating and Naming Military Aerospace Vehicles:

4.1. Designator Definition:
4.1.1.The  MDS designator is an official DoD recognized alpha-numeric symbol designation of a military defense aerospace vehicle. .... The designator describes the aerospace vehicle in two components where the components are separated by a hash.The first component, comprised  only  of  alpha characters, describes the mission of the vehicle.The second component, comprised of both alpha-numeric characters, describes the design number and design series of the vehicle.
4.1.2. Standard  aircraft MDS designators are comprised of the following: status prefix(optional), modified mission(optional), basic mission(required), design number (required), design series (required).

The document also gives some examples of this implemenatation:

Both tables from Designating and Naming Military Aerospace Vehicles
The 1962 system replaced the earlier system, where each service had their own systems in place for naming of aircraft.

From 1924 - 1962, the USAF (and the USAAF before them) used the 1924 United States Army Air Service aircraft designation system.

During the same time, the USN used the 1922 United States Navy aircraft designation system.

Once the USAF was formed from the USAAF in 1947, the US Army followed the 1956 United States Army aircraft designation system till 1962.

Before all of these was the 1919 United States Army Air Service aircraft designation system.

More details about the aircraft designation can be found in this page.
Basically, the counters were reset while the 1962 sytem was adopted, leading to unrelated sets of aircraft numbering. As for individual aircraft numbering, there has been a number of cases where the system was not followed, like the F-117 Nighthawk.
Adherence to this system has been patchy at best. So, you have B-1 Lancer and B-2 Spirit after B-52 Stratofortress (this was due to the counters being reset), while the next bomber has been named B-21 Raider.

And what are the usual missions of the vehicle that gives the first component, comprised only of alpha characters? F for fighter? B for Bomber? W for weather?

@Marine1 Yes. A for  attack, B for Bomber, C for transport etc. It's in attachment 3 of the linked document.


text:
What is the history of this specific Cessna propeller (s/n F2430)?
Hoping someone can help... I'm looking to get some information about a Cessna plane propeller my Fiancé recently bought. It's his birthday coming up and it would be great to have any sort of history, photos or further info on his pride and joy.. The information on the propeller:
Cessna KLIPTIP
MET-L-PROP
MCAULEY, DAYTON OHIO
SERIAL NO- F2430
DESIGN 1A100 MCM 6950
T.C 918 P.C.3
I do have photos if necessary
I really would appreciate any sort of help - it would be great to give him a surprise.

That may help to start: 1A100 MCM 6950. FAA TC P-918. Likely from a C150 (A-F). Looking at the time you posted the question, you may live in Europe and also have bought the propeller here. If so the aircraft may have been built in France by Reims Aviation.

Have you tried contacting Cessna or McCauley directly? They might have info on what aircraft it was originally installed on.


text:
Are test pilots who work for the FAA paid on the GSE pay tables?
Many employees of the US federal government are paid according to the GSE salary tables. Are the FAA test pilots paid on the same table? For example someone could be in the grade 14 step 6 rate. Or, are they paid according to some other pay table?

Not exactly. Few if any FAA employees are paid on the General Schedule. Instead, the FAA has its own pay plans:

Core Compensation Plan (FV)
Air Traffic Compensation Plan (AT)
Executive Compensation Plan (EV)
FG Pay Plan
Similar to the Federal General Schedule (GS), applies to mainly salaried employees whose positions have not yet been converted to the Core Compensation Plan.
FW Pay Plan

As an example, here is a job announcement for an "Airspace System Inspection Pilot" based in Anchorage, AK. The position is on the FG pay plan, as an FG-13 or FG-14.

Yes, FAA test pilots are paid based on the General Schedule for the levels of GS-1 through GS-18.
If you are interested in reading the job description, one can be found on AvJobs.
The relevant section for pay is this one:

Wages and Benefits
Most Federal Civil Service employees in the aviation field are covered by the General Schedule and their salaries vary according to their grade level (GS-1 through GS-18). Within each of the grades provided in the General Schedule, provision is made for periodic pay increases based on an acceptable level of performance. With an acceptable level of competence, the waiting period of advancement to steps two, three and four is one year, steps five, six and seven is two years, steps eight, nine and ten is three years. The starting grade is normally GS-7. Trainees are paid while learning their jobs.

  The entry level is GS-9. Entrance salary will vary with the degree of the applicant's experience and training.

Not exactly true; the FAA has an FG pay plan which is similar to the General Schedule. For objective questions like this it is better to go to the source directly rather than third-party sites like AvJobs.

I'm not aware of the FAA having a corps of test pilots; that's usually the domain of the OEMs themselves who have their own private test pilots employed by them.  Military test pilots are paid at their officer rank grade level.  NASA also has test pilots who work for them, who are paid on the GS pay grades, generally a GS 12-13 job for starters.

The FAA does have test pilots.

all_licenses: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/


text:
What effect would a afterburner have on the compressor if the nozzle outlet is not increased?
In order to operate an afterburner, it is necessary to adapt the nozzle outlet area. As far as I understand it is necessary to open up the nozzle when the afterburner is increasing its temperature or the mass flow rate would decrease. It is also necessary to close the nozzle when the afterburner cooling down or the turbine would rev up and exceed the critical rpm.

Now, what I want to know is what happens with the compressor if the outlet area is not adapted?

If the afterburner temperature increases and the nozzle is not adapted I guess that the compressor will reduce its normalized rpm $u/\sqrt{\gamma R T}$ because of the reduced mass flow rate and it will also come close to a compressor stall (surge).
Is it right that the compressor rpm is reduced or does it stay the same and the mass flow rate gets throttled?

Yes, when the AB is lit, the nozzle needs to be opened, because the increase in exhaust temperature causes a decrease in density (pressure remains about the same), and so the same mass flow needs a bigger nozzle area to flow through. In AB, the engine mass flow is about the same as in max dry operation. The AB basically sits behind the core, and operates more or less independently, because the change in nozzle area compensates for the change in exhaust temperature.
And you are exactly correct, if the nozzle wasn't reduced when the AB is turned off, the spools would over speed.
If the nozzle area wasn't increased, the sudden lighting of the AB would most likely stall the engine - probably the fan as the back pressure wave can easily travel back up the bypass duct. AB stalls were common on first generation low bypass military engines. If you could light the AB slowly, it should just cause the spools to slow down, and mass flow to correspondingly decrease. Modern ABs light a bit progressively, to give a "soft" light. Older designs weren't quite so refined.
E.g. See page 208:

The TF30 ... still had compressor problems going in and out of afterburner..

And here about the F100 saying:

Some stagnation stalls were caused by "hard" afterburner lights, which were mini explosions that took place inside the afterburner when it was lit up. The pressure wave from the explosion then propagated forward through the duct to the fan, causing the fan to stall and sometimes even causing the forward compressor stage to stall as well. These types of stagnation stalls usually occurred at high altitudes and at high Mach numbers.

Also read Goodbye F100 Stagnation Stalls, see:

To reduce the influence of pressure waves traveling back up the fan duct, the compressor inlet lip has been moved to bring it closer to the rear of the fan.

+1 for your answer. but what happens with the compressor if the area is not adapted? Does the compressor change its normalized rpm $u/\sqrt{\gamma R T}$?

@MrYouMath. If the nozzle area isn't adapted, the abrupt lighting causes a pressure wave that travels back up the bypass duct, and stalls the fan. If you could light the AB really slowly, yes, in theory, rpm and mass flow would adapt.


text:
Where can I find a list of rules of thumb formulas for navigation?
Is there any list of formulas for quick counting navigational parameters of the flight, if navigational computer is malfunctioned.
For example, I need to recalculate how long can I fly, if the wind is changed.

There is no short list but almost all the navigation information you could ever want can be found in this handbook published by the FAA. If you are worried about your nav computer failing you can always get an E6B which is about as close to failure proof as you can get. An E6B will expedite most most nav related calculations in the air (like headwind component). My E6B has some common nav calculations written on the back of it actually.

Is this a common device in todays airlines? (E6B)

The chances all the nav computers, tablets and now pilots smart phones go out is slim so I doubt they carry E6B's any more but Im sure some still do if for anything out of habit.

@wiaim I don't know if it's "common", but I always carried an E6B in my flight bag. My dad, who just retired from FedEx after being there since 1978, also carried one with him his entire career. I don't think he ever needed to use it, but he had it just in case. And it doesn't exactly take up a lot of room or weight in a bag.

Even today, I teach using a mechanical e6b, and I require that my students be proficient with it. The results are visual and intuitive and often people miss a keystroke and find themselves heading on a course of 020 instead of 200. If they choose to use an electronic calculator afterwards that is their choice period but I insist that they learn how to use a manual E6B and use it for all primary training and cross country flights.

This is not exactly a "rule of thumb" site, but a friend has put together aviation formulas for the last several decades, available at: http://www.edwilliams.org/avform.htm
Rules of thumb for navigation are different, and while I have probably 40 books on navigation alone, the rules of thumb are distributed among them.  As technology changes, the rules also morph.  For example, rules specific to NDB and ADF navigation are almost obsolete these days, and have low relevance to most pilots.
Meanwhile you will find a collection of formulas in the above reference. And the FAA publication @Dave mentioned will be an excellent general read.


text:
What should I do with aileron reversal?
During high speed flight, any aileron deflection may cause the wing to twist about its torsional axis (aileron reversal).
Is it dangerous?
In what kind of conditions this occurs, what have I do as a pilot to deal with it or prevent it?
What speed should be for aileron reversal in transport type of aircraft(average)

I reckon this should be the aircraft designer's concern rather than the pilot's. As far as I know big airliners use spoilers instead of ailerons at high speeds to avoid aeroelastic issues, but this should be managed automatically by the flight control system. Smaller aircraft should not encounter such issues within their allowed flight envelope.

@mezzanaccio or they use a different sets of ailerons (high-speed ailerons) usually located nearer to the fuselage, sometimes over the engines (look at B767, B777 or MD-11 for example) :-)

Unless you're a test pilot, you're unlikely to encounter such situation when you fly. The operating limitations are established for a reason. You have to be way outside the certified flight envelope for this to occur.

Yes, this is dangerous and must be avoided.
Consider this: Between the low speed range where the aileron works as intended and the high speed range where it works like a Flettner flap there is one speed point where the rolling moments of the aileron and the wing twist cancel each other out. There the aircraft is uncontrollable in roll. No sane pilot would fly such an aircraft voluntarily.
Set the speed at which full aileron deflection produces only a quarter of the rolling moment coefficient as the never exceed speed.


text:
How can a pilot anticipate cloud formation?
I read a few articles and a book about cloud forming, but I didn't really understand it.
Can anybody explain in simple terms how clouds form?
As a pilot, what factors that contribute to cloud formation can I anticipate?
Where do the terms Saturated Adiabatic Lapse Rate (SALR), Dry Adiabatic Lapse Rate  (DALR), Environmental Lapse Rate (ELR) and dewpoint fit into it all?

This question is being discussed on meta.

Clouds can be formed in many different ways. Before we go through them, we need to establish some basic facts.
Clouds are made up of liquid water, or solid ice. Clouds are not water vapour; vapour is a gas and is invisible. Once more, because this is important: clouds are liquid water, not water vapour.
Water droplets in clouds are extremely small. Clouds are visible because light is scattered in these droplets. The water droplets can stay suspended in the sky due to friction and air currents.
In order for water vapour to condense into liquid water droplets, to form clouds, condensation nuclei must be present. This can be tiny particles of dust or other impurities around which water droplets can form. This is where the idea of human cloud generation comes form - by adding condensation nuclei to the atmosphere, clouds are more likely to form.
A mass of air can contain a certain amount of water vapour (=gas). The maximum amount depends on several factors, of which the most important one is temperature. Cold air can contain less water vapour than warm air. If more water vapour is present than the air can contain, the water has to condense (the opposite of evaporate), to form water droplets - clouds.
So, how are clouds formed then?
By adding moisture
Air can only contain a certain amount of water vapour. If we try to add more water vapour to the air, it "won't fit". As a result, the water vapour will condense, forming visible water droplets - clouds. This can happen over a surface of water during a warm day, when surface water evaporates. The air won't be able to absorb the evaporated water, so instead it has to become liquid.
Cooling from below (advection)
Warm air can contain more water vapour than cold air. When a warm, moist airmass moves over a cold surface, the temperature of the air will drop. When reaching a certain temperature, the air becomes saturated - it contains exactly as much water vapour as it possible can. We call this temperature the dew point. If the air is cooled further, some of the water vapour in the air has to condense into water droplets. Imagine squeezing a saturated sponge - the water has to come out.
Adiabatic cooling (convection)
On a sunny day, the sun will heat up the surface of the earth. Because the surface is not uniform, it will heat up at different rates. A sandy field will get much warmer than a wet area, for example. The air directly above such hot areas will also be heated up, by radiation from the surface. Hot air has a lower density than cold air, so at some point it will start to rise ("heat rises"). As this warm bubble of air rises, it will start to expand. This is because pressure drops with altitude. As the air expands, it will cool off. Now we're back at the basic principle that cold air can hold less water vapour than hot air. As our bubble of air rises, and cools down, at some point, it will reach the dew point, and a cloud will form.
The adiabatic lapse rate is the rate at which a bubble of rising air will cool off with altitude. Rising air will cool with approximately 3 degrees C per 1,000 ft of altitude gain (dry adiabatic lapse rate - DALR), simply because it expands as a result of the lower pressure. When air starts to condense, and a cloud forms, this process releases latent heat. Simply put, it took energy to make the water evaporate, and this energy is released again when the water condenses. This means that once our bubble of rising air reaches the dew point, and a cloud starts to form, it will actually cool off slower. The saturated adiabatic lapse rate (SALR) is approximately 1.5 degrees C per 1,000 ft.
Now, for how long will our bubble of air keep rising? It will keep rising as long as the air surrounding it is cooler than itself. The general temperature of the atmosphere at a given location is known as the enviromental lapse rate - ELR or ELT. As long as the DALR is less than the ELR up to the dew point, rising air will form clouds.
Frontal lifting
A warm front is when a mass of warm air moves forwards, displacing a mass of colder air. Since warm air has a lower density than cold air, when the two air masses meet, the warm air will be forced upwards, above the cold air. This causes the air to expand, and cool. As this happens, the air might reach the dew point, and clouds will be formed.
Orographic lift
Orographic lift is quite similar to frontal lift. Instead of being forced up by cold air below, an air mass is forced upwards by terrain (i.e. wind blowing towards a mountain). Then it's the same old story - the air rises, expands, cools and water vapour condenses.
Turbulence and convergence
Mechanical turbulence, for example due to rough terrain, can cause vertical movements in the atmosphere. If these are large enough, air can be forced upwards, which, as we now know, will form a cloud.
Convergence is when two air masses move towards each other, creating a vertical stream of air in the middle. This column of air moves upwards, and clouds are formed.
These are the basics of cloud formation. As you can see, they all depend on the same basic principles that I covered in the beginning of this answer.


text:
Where can I find references that directly relate drag coefficient increases to passenger capacity reductions?
In these notes, the authors state that:

On the Concorde, a one count drag increase (∆CD = .0001) requires two
  passengers, out of the 90 ∼ 100 passenger capacity, be taken off the
  North Atlantic run.

and refer to this article (paywalled). I've seen other statements that an increase of one drag count is equivalent to 5-10 passengers, but do not recall the source.
Do you know of any other references that list the equivalence between drag count increases with reduced numbers of passengers?

Your question is not completely clear to me. You want an equation that compute the relation between drag coefficient and number of passengers?

I do not understand the question and I don't understand the answer.  Perhaps knowing the reason for the question (research?) would help.

@Gianni Alessandro: I think my question is quite clear - I am asking for references that give examples of how increased drag counts (higher than expected drag coefficients) forced the manufacturer to drop the number of passengers to keep the aircraft range. I did not ask for an equation. It seems pretty clear to me that the relevant equation is the Breguet range equation. Just what is not clear about my question?

@user6035379: I don't see how the motivation for asking the question makes any difference to understanding it, but my motivation is simply curiosity, not research.

@user1362373 there are two people commenting and one person answering that didn't understand your question. You may be simply less arrogant and try to make it clearer to somebody that is freely trying to help you.

@Gianni Alessandro: I don't think I'm being arrogant. I asked you what was not clear about my question since it seems clear to me, also after rereading it.

@user1362373 Ok, maybe I misinterpreted you, I will try to give you my opinion. Number of passengers and Drag coefficient are not directly intercorrelated or, you can also say, they are intercorrelater through a chain of parametres so complex that it is not practicable to write it in a single equation.
So we asked you: why do you ask this? Why do you ask this question, what exactly do you want to know? Which is the aim of your question?

The book "Airplane Design Part I: Preliminary Sizing of Airplanes" by Jan Roskam covers this extensively.
Nothing tabulated, mind you but the text goes into extensive detail of the equations involved for the sizing of a prospective aircraft and the relationships between the aircraft range, drag polars under various flight conditions and payload weights.
It also gives the equations for calculating the sensitivity of the change of aircraft range with drag polar and payload weight, which is essentially what your passenger is.
EDIT
Relevant section is in chapter 2 from page 74 onwards.Problem 1 on page 85 is practically custom tailored for your needs here.
Bear in mind there is no one size fits all application of a rule of thumb for this question as every aircraft will differ on account of any number of factors.

Thanks for your answer. I'm aware that the Breguet range equation can be used to see how increased drag results in reduced payload (reduced number of passengers). But in order to use that equation, quite a lot of information about the aircraft performance is required (CL, CD, SFC, etc). Therefore, I did not ask about the equation, but about the actual result: How increases in drag coefficients result in reduced number of passengers.

In the book Roskam does some regression modelling of aircraft of similar roles to come up with a couple of coefficients for use in some of the other (non breguet) equations. The Cd values can likewise be assumed or educated guesses made.

I'll take a look at Roskam's book, thanks.


text:
Is there an online source of active flight plans?
Is there a way I can look up flight plans filed in the United States? I tracked an aircraft on Flightradar24 and I would like to be able to find it's flight plan in some sort of database.

It seems you are looking for domestic flights in the US. The FAA database is not public.
You can use ADS-B tracking sites to look at the route. Remember instructions after takeoff (departure and transition) and before landing (transition and approach) are determined late and can be changed, depending on winds and other parameters.
E.g. on Flight Aware, for JBU124 between LAX and JFK, the route is mentioned:

and can be decoded:

These sites also create route history records. After a certain number of days, it's paying.

Data is not public. That's what I was looking for. Thanks.

In the US, flight plans don't go through the FAA at all, it is handled by LEIDOS, formerly Lockheed Martin Flight Services under federal contract.

@RonBeyer: Indeed FAA subcontracts to Leidos, Lockheed Martin... as many other. services.  But the service is still a FAA one. Nasa does the same, the Shuttle is still a Nasa spacecraft.

The FAA has a great database. You should find what you are looking for. @mins you are right.

So FlightAware just infers based on location that it was using various VORs? Or does it somehow get the route ahead of time?

@aidanh010: The planned route you see comes from the flight plan (FlightAware has access to flight plans filed at ANSP like Eurocontrol or FAA), the actual position comes from multiples sources, ANSP but also private ADS-B receivers (including multilateration). FlightAware started providing tracking data by only sharing private ADS-B output between subscribers.


text:
In which direction should a turn-back be made after an engine failure on a multi engined airplane after take off?
In case one of the engines fails after taking off (let's suppose the left engine is the one that fails), which direction should we turn to go back to the airport? A left or a right traffic pattern?

Right pattern! Always, always turn away from the dead engine. See here for more.

Unless you have allowed airspeed to degrade to unsafe levels, turns in either direction are fine.  If you're uncomfortable turning into a dead engine it may be worth practicing SE maneuvers to become more familiar with SE handling.  Locking into a hard if-then now will put unnecessary limitations on your decision tree should you encounter a real engine failure at some point down the line.

As acpilot states, turns in either direction can be fine. The key is fly the airplane at or above the appropriate airspeeds. There are valid reasons to avoid or to choose either direction in different cases. Statements to the contrary are naive and likely typically come from those with little or no experience with piloting multi-engine aircraft in emergency scenarios.

This question is not a duplicate. The other question only asks about why turns into the inoperative engine should be avoided. This question validly broadens the issue to consider both sides. This question is helpful, and should remain open.

The reason to not turn into a dead engine, is that that is the direction the plane wants to go. You will easily enter the turn, but might very well overdo it, or find yourself unable to exit the turn. Turning away from the dead engine is much harder, but is much less likely to fail catastrophically.

That  depends on a lot of factors. Are you declaring an emergency? What altitude are you at what speed are you at when this happens etc?   What kind of aircraft are you flying? Does it have enough power to continue to climb on one engine? Some trainers do not.
For a typical airliner, loss of a single engine is not a big deal. The pilot will simply declare an emergency and get vectors from controllers as to where to go land again. Most airliners have plenty of power with one engine out and they don't have to worry about that. Smaller twin engined GA aircraft are a different story and may not be able to achieve a positive rate of climb on one engine, especially with the gear and flaps extended just after liftoff.  At low altitudes where this performance factor may be the case for the specific airplane you are flying, you may have to execute a forced landing in a clearing either directly ahead or off to your side, as a 180 deg turn to the airfield would be suicide.
As to maneuvering once an engine is lost, there is no requirement for this, save a pre-determined VFR traffic patterns for the departure airport.
If the engine out is an emergency and you cannot comply with either a controller's instructions or uncontrolled procedures, you are authorized as PIC to disregard any regulation as required to deal with the emergency.  This means any kind of maneuvering you feel will safely bring the aircraft back to the ground is acceptable.
I've read a lot of posts and comments amongst pilots about not turning into a dead engine on a twin; this is nonsense with one caveat - you must have sufficient airspeed in order to do this.  It depends on the aircraft in question but a good rule of thumb is that if you are at or above Vyse you can GENTLY turn into a dead engine.  The threat comes in attempting to turn into the dead engine at or near Vmc, minimum controllable airspeed on a single engine, where it may not be possible to arrest the turn due to thrust asymmetry.

Another variable might be terrain. I fly in a lot of places where terrain could make turns in one direction prohibitive. An engine failure in such a place might necessitate a turn in a specific direction regardless of which engine failed.

Don't turn into the dead engine, turn away from it, you have to keep the dead engine in front of the live one otherwise loss of control can occur at low speeds.
I assume you can maintain height / have sufficient altitude and are at or above blue line speed if you are considering turning because some height may be lost in the turn. Some twins can only just about maintain height on one engine depending on aircraft loading etc. If you are low / only just at blue line you should seriously consider closing the throttle on the good engine and trying to make the best of a bad job or extend out and see if you can gain some height first before doing anything rash. Hopefully extending out might allow you to find a suitable place to put the aircraft down. This is far preferable to stalling and spinning trying to make the runway at low speed / low height.

I'm assuming you are in a light twin. If you are in a jet you should have a lot of excess performance and would usually take your time and extend out assuming the aircraft wasn't in immediate danger, e.g. wing on fire and burn off excess fuel etc. (Don't shoot - I'm not an airline pilot).


text:
Can an F-16 fly with conventional hydraulic powered controls without a computer controlled Fly By Wire System?
Radio Controlled models of F-16s fly fine without computer controlled flight systems. Apparently these model aircraft are not unstable in pitch but probably positive in pitch stability. There may be trade offs in high AoA capability but it would seem that an F-16 with sufficiently forward CG would be able to fly using conventional or hydraulic controls like for example the F-4 or F-5.

I did some searching and got an extremely interesting answer here:
By the way, I should have worded my question differently :  the F-16 does have hydraulically powered controls, but the pilot inputs are sent through a computer first.

They designed the plane so it could be fitted with conventional
  hydro-mechanical controls if the fly-by-wire system couldn’t be made
  to work acceptably. “We spaced the bulkheads so that we could move the
  wing back and have a statically-stable airplane,” says Hillaker. “We
  were just giving ourselves some insurance. The wing would have had to
  have been moved back eighteen inches. All we had to do was make the
  two bulkheads have the same load capacity. One of them that we
  would’ve moved the wing to was higher than it needed to be, unless you
  moved the wing back.”  The structural differences carried over to the
  production F-16 design, but fortunately were never needed. The
  fly-by-wire system’s control problems were quickly ironed out and the
  plane, even with all its advanced features, steadily gained support
  both in the U.S. and abroad

So model makers note: get the CG for the F-16 and move it back 18 inches or whatever the equivalent is on your model for a stable airplane.
http://www.f-16.net/articles_article13.html

Well an RC model is going to have a different center of mass point than the real thing.  Second, an F-16 is actually dynamically stable in subsonic flight; it requires a flight control computer for transonic and supersonic flight due to the shift in the center of pressure on the wings during this transition.

The F-16 is said to have 'relaxed stability' in flight, for transonic and supersonic flight the all moving tail plane would probably be used to trim the plane for flight, as is done on the non- fly by wire F-5 and T-38 Talon.

But every supersonic airplane experiences such a shift. It then requires a different balance (trim) and control ratios (from stick to elevator) to have acceptable handling. A computer is handy for that (as long as it has guaranteed reliability), but in fact the airplane becomes more stable at supersonic, and thus could be handled conventionally. A stability augmentation system per se is needed mostly for subsonic flight.

Actually, some model aircraft use a "computer system" similar to the real thing, only much more simple. They have gyros that detect the attitude of the aircraft and the inputs of the pilot to determine if the maneuver was intentional, or due to some outside force, and will counter it as needed.


text:
Is the induced drag independent of wing span?
I am a new aviation student and I was reading about induced drag the other day. I know that it is produced as a result of the tip vortices and that the greater the aspect ratio of an airplane the less the induced drag force. But when it came to the equation of the force, it is equal to:
$D_i = \frac{1}{2}\rho V^2 S \frac{C_L^2}{\pi  AR \epsilon}$
If we substitute aspect ratio $AR$ with span/chord $\frac{b}{c}$  and plan area $S$ as $b\cdot c$, the span term will be cancelled and the induced drag will be affected by the chord length only.
It kind of contradicts the effect of aspect ratio on the induced drag force, doesn't it?

See http://aviation.stackexchange.com/a/8797/4197

Aspect ratio $AR$ can be written as $\frac{b}{c}$ which is equal to $\frac{b^2}{S}$.
Before we start substituting, note that $C_L$ also depends on the wing surface area $S$.
$L = \frac{1}{2}\rho V^2 C_L S$
or
$C_L =  \frac{L }{\frac{1}{2} \rho V^2 S}$
Substituting all this in the induced drag formula yields:
$D_i = \frac{1}{2}\rho V^2 S \frac{C_L^2}{\pi  AR \epsilon} =
\frac{L^2}{\frac{1}{2}\rho V^2 S \pi AR \epsilon} = \frac{L^2}{\frac{1}{2}\rho V^2   \pi b^2 \epsilon}$
This shows that the induced drag is proportional to the inverse of the square of the wingspan.

Let's work this through...
The coefficient of induced drag is inversely proportional to the aspect ratio.
$C_{di} = \frac{C_L^2}{\pi  AR e}$
NASA Page on induced drag coefficient
The overall coefficient of drag is the form/skin drag plus the induced.
$C_D = C_{d0}  +  C_{di}$
NASA Page on drag formula
The actual force of drag assuming $C_{d0} = 0$ is
$D = \frac{1}{2}\rho V^2 S \frac{C_L^2}{\pi  AR e}$
Can be reduced to
$D = \frac{1}{2}\rho V^2 c^2 \frac{C_L^2}{\pi  e}$
Where $c$ is the mean chord.
As DeltaLima pointed out in their answer, you could then substitute $C_L$ using the lift equation to show it is inversely proportional to the span squared.
Both equations are correct so what we can take away is:

As the chord is increased induced drag increases
As the span is increased induced drag decreases

In other words, the induced drag is inversely proportional to the aspect ratio.

May I disagree with your first conclusion? If lift stays constant, increasing chord will decrease lift coefficient, so induced drag will not be affected. Only the induced drag coefficient is inversely proportional to aspect ratio. Induced drag is inversely proportional to span loading.

@PeterKämpf I thought it was the other way around, the coefficient was constant and the lift changes?

If lift changes, drag has to change, too. The goal should be to not change lift, so you can see what the parameter change does to drag.

@PeterKämpf but to me that's the point of the question, the does the drag change? Unless I'm mistaken (entirely possible), if we kept the aerofoil shape the same and just increased the size (chord length), the lift would change not the coefficient of lift.

Yes, you are not mistaken. In the context of your question the first conclusion is correct, even trivially so. But it plants a wrong idea about induced drag into the mind - just what prompted the question in the first place. If you look at a real airplane and play with the parameters, a chord increase will reduce angle of attack and result in constant induced drag. From there it becomes easier to see that span loading determines induced drag, not chord.

As we know that induced drag is due to vortex generated due to pressure diffrence at chord.So if the chord is longer more induced drag will be produced.From mathematical equations we can say that coefficient of induced drag depend on A.R while total induced drag doesn't depend on A.R

Could you include those mathematical equations in your answer?


text:
Do all Fuselage sections have same performances?

The Burnelli machines had an airfoil shaped fuselage;

some indicate near 10% of lift in a 21 century airliner comes from
fuselage;    'Flying Wing' concept is old, and still attracts many;

bottom of SR-71 looks shapen as a high speed race boat;

at very high speeds, air is thick, not as a brick, but as
'marmelade', it's a Reynolds Number affair, this figure, you know,
expresses relations of inertia and viscosity forces inside a fluid.

Would a flat bottomed fuselage add even more lift than the regular round section, increasing the overall fuel economy of an airplane? Does the concept deserve Aerodynamic Wind Tunnel testing?
[]

Likely the answers you're looking for: Why are there no blended-wing passenger airplanes in operation?

No, 'Blended wings' are similar to some German Wartime projekts, Delta, Double Delta, with engines on upper side, rear side of wing,  what I was asking about is an ordinary airliner with a semicircular section in a common lenght cabin, to provide more lift than the regular cylinder, round or oval section, sorry for not detailing the question enough as to dissipate any doubt. Blessings +

"Would a flat bottomed fuselage add even more lift than the regular round section, increasing the overall fuel economy of an airplane?": In answers you have some clues about the fuselage section, e.g. "The fuselage has a round cross section, because that is the lightest form of pressure vessel we can make. Tilt it, and it provides some lift as well"

Yes, this is known, what I asked is if a flat bottomed, semicircular fuselage section would provide more lift, thus increasing overall airplane efficency and fuel economy, while keeping the passenger and cargo capacity, and the structural strenght. Thanks. Blessings +

Where are you going to put the luggage?

Between floor and bottom, you can get space as needed, but yours is a good objection. The fins added to my sketch wanted having the effects of winglets in reducing drag. This could be tested in an scale model at an aerodynamic wind tunnel, but I lack both the tunnel and the funds. For fuel, the X-15 side tanks are convenient, if it were tolerable at hypersonic speeds, for sure will be in airliners. Blessings +

The goal isn't more lift, the goal is high lift-to-drag ratio.

Induced drag is minimized by following elliptic distribution of lift over span, that is fairly constant lift over span in the middle, decreasing towards the wingtips. To achieve that the fuselage in the middle needs to only produce as much lift per its width as the wing roots next to it, which means relatively very little for its size. The circular fuselage can already do that.
Form drag is minimized by keeping the cross-section low. A tube has low cross-section for volume.

The other goal is to minimize the structural weight so more capacity remains for the payload.

Tube has small surface (so less skin needed) and large strength for volume. Any flattening would increase the relative surface and reduce strength, requiring more weight in structural reinforcements.

The traditional design fits these constraints really well.

Draw in the "fuselage section" in red (equal volume) with the flying wing and you have your answer.
At high subsonic speeds, lift isn't the issue, form drag is.  Supercritical wings have evolved to the point where they are actually flattened on top to avoid shockwave drag.  These aircraft literally "surf" along on their undersides, so flattening the underside of the fuselage has merit.
However, the wing of the average airliner is already too big for high subsonic flight, as it must be engineered for lower speed approaches and landings (and also must be fitted with Fowler flaps and slats).
Drag at cruise speed, carrying the same weight, is why general airliner design differs little from the Boeing 707 of the late 1950s.
Advances have been mainly in increasing wing aspect ratio and engine efficiency.  We can see a smaller tail, further back on a longer, thinner fuselage, will generate less drag at high subsonic cruising speeds, until proven otherwise.


text:
Could the toilet be used as an extra passenger seat?
In the US, if the toilet had a seat belt, would it be legal for an airline to board one more passenger than the number of normal passenger seats, requiring that whoever used the toilet last must remain there until the next person needs to use it?
Inspired by: "A new engine inlet reduces vibration and cabin noise, the lavatory receives a belted seat allowing a fifth passenger and the Garmin G3000 gets computed take-off distance and stability/angle of attack protection."  -- HondaJet Elite
Related Embraer Phenom 100

Does that seat have a window?

So any passenger using the toilet can't return to their seat and sit with their travelling companions? It sounds awful, but I'm sure that Ryanair would love it.

Who goes first?

This is not new. Many business aircraft have seat belts on the toilet seat.

Please don't give the budget airlines ideas...

Most bizjets have very little room aboard, so they have to choose between lavatory seating and emergency lavatories located under normal seats. Emergency lavatories are a subject of some horror stories rivaling Stephen King himself.
So, a small bizjet lavatory is rarely the same thing as a restroom aboard a passenger jet. The usual idea is to try not to use it at all, except when the only alternative is worse.
The Hondajet is unusual in offering a luxury as lavish as a fully enclosed restroom in such small a size. Still, it's a luxury, competing with extra seating, with the expected result of getting jump seat certification for extra flexibility. You wouldn't use that seat for the owner or their guests, but rather for staff or cabin crew.
If a commercial toilet on an airliner gets equipped with a seat belt, that seat will also be used as a jump seat for the crew. Some part of the cabin is already spent on providing crew seats, so that would get redistributed to revenue seating, and crew moved to the "new" seats. Needless to say few are looking forward to it.

I laughed so hard at the horror story that I cried!  Hahaha!  The poor fellow...

When I was with Weber Aircraft we provided many lavatories for Boeing aircraft.  There was never any requirement for a passenger in the lav during structural tests/qualification.  Based on this I know that it would be illegal for have someone in the lav during takeoff or landing as it would exceed the structural qual test requirements.


text:
How can the lift force be changed without changing velocity?
I am facing a problem for calculating the 4 forces affecting the aircraft balance.
Suppose the following inputs:
Aircraft velocity is 222 m/s.
Aircraft mass is 23500 kg.
Aircraft weight is 227360 kg.m/s2
At zero angle of attack the lift coefficient is 0.2
By Calculating the lift force from one wing 172899 N.
for the two wings lift force *2 = 345799.125 N
The problem is:
Now I want the aircraft to go to balance state to move with constant velocity.
So all the four forces should equals to zero thus the lift force should equlas the weight force.
How Can I decrease the lift force?
Assuming:
I still need the aircraft to move with constant velocity 222 m/s.
The lift is affected by angle of attack which is zero.
The air density is constant.
how can I the aircraft balanced with velocity 222 m/s?
Can I decrease the lift force without affecting the velocity?

"How Can I decrease the lift force?" Typically when flying this is done by lowering the AoA until lift=weight and the aircraft holds altitude. I would think that you would want to pick an AoA to be the lowest drag at your cruise speed, which will give you the highest velocity for the least amount of power.

Thanks very much. I don't know that small decrease in the AOA will make this big difference in the lift force.

The coefficient of lift increases by about 0.1 or a bit more per degree.

Is your airplane a biplane? Then the total lift will not be double due to interference. If it's a normal monoplane, it has only one wing, left and right halves. Moreover, lift calculation normally involves the full wing area, which usually even includes the part occupied by fuselage. Rarely do we use half wing area for anything.
I mean, people do say "left wing", but when you are so exact with your numbers and units, you want to be precise with the terminology ;)

The problem is:
  Now I want the aircraft to go to balance state to move with constant velocity.
  So all the four forces should equals to zero thus the lift force should equlas the weight force.
  How Can I decrease the lift force?

This can be done by simultaneously reducing AoA (which in-turn reduce CL) by introducing little down elevator and reducing the engine power accordingly to maintain the airspeed.


text:
Can composite materials be used on super-sonic aircraft?
Can composite materials be used in aircraft that can fly super sonic.

Where? There are certain places that the answer is absolutely yes, and others that the answer is absolutely not.

Sure. Almost all the modern supersonic combat aircraft incorporate a significant amount of composites in their construction. For example, in case of Dassault rafale:

Composite materials are extensively used in the RAFALE and they account for 70% of the wetted area.

though they account for only 28% of the structural weight. This is in line with other aircraft- for example, composites contribute to around 25% of the weight of F-22 Raptor.

Dassault Rafale structural materials; image from indiandefence.com
You can see that the composites are extensively used in the wings, where the skins are made usually with composites, which enables them to be made in a single piece. The composite materials are superior to the metals used in aircraft in a number of performance parameters. The offer better strength to weight ratio and corrosion resistance, among others. According to Dassault,

The RAFALE composite wing weighs the same as the MIRAGE 2000 metallic wing, but is 10% larger and can sustain a load that is 20% greater.

Composite materials are being used increasingly more and more in case of high performance aircraft- not only in wings (and radomes, where they have been used traditionally) but also in interior load carrying members, which have been usually made from metals. Even in case of Rafale, the wing box is made from carbon fiber composite. Another reason for using composites, atleast in combat aircraft is for stealth.
There are other areas in structural design, where the metals are better, for example, in impact resistance and in high temperature areas, where titanium is extensively used. Still in other places like landing gear, steel is used. The image below shows the use of various materials in F-22 Raptor.

Materials used in F-22 Raptor; image from allstar.fiu.edu
Again, the distribution is similar- composites make up majority of the wetted area while a minority of structural weight. In the end, the use of composites or metals are determined by their location and intended use.


text:
What are typical airspeeds and lift coefficients for UAVs at different flight stages?
I've been trying (unsuccessfully) to figure out the relationship between airspeed of a fixed wing UAV at different flight stages. What I mean is, I would like to know the order of airspeeds from largest to smallest that would be expected for an aircraft (in particular an UAV with say 5m wingspan) to have during climb, cruise and descent. For example, the answer I'm looking for is something like: from largest to smallest, airspeed is expected to be ordered like this -> cruise>climb>descent (this would be my guess by the way).
Also I know that lift coefficient varies with angle of attack, airspeed and air density, but is it possible to make such a qualitative analysis to find an expected ordering like this for different flight stages? Looking only at the relationship between lift coefficient and airspeed, according to my previous guess, I would expect the lift coefficient to be smaller during cruise and larger during climb and descent. Is this correct?

It is a function of the airfoil design.  If you have an airfoil in mind, this is an easily answered question.  If you have an airframe defined, it is a much more precisely answerable question.

Your answer relates to the lift coefficient part right? Or is the climb velocity and cruise velocity also dependent on airfoil/airframe configuration? I was wondering if, in general, aircraft tend to travel at higher airspeeds during climb or cruise?

I reread your question several times, and will attempt to answer. Hopefully I understand you correctly. First, for largest speed to smallest, I would order descent>cruise>climb.  The way to think of it is that during a climb, you are building potential energy (altitude).  When that energy plateaus at your cruise altitude, you stop investing in potential energy, and maximize your kinetic energy (cruise speed).  During descent, there is energy to bleed, because you are lowering your potential energy (altitude) and converting it to kinetic energy (descent speed).
The gross assumption is that your UAV power setting remains about the same during all three phases of flight.
In this example, the lift is greatest during the climb, when you are investing in potential energy, and not using as much kinetic energy.
The descent would have the lowest lift, because you are willing to trade potential energy for kinetic energy, and the altitude decreases and the speed increases.
Forget my original comment, I don't think I understood your question at that time.

Just to give you a conceptual speed value set: climb 50, cruise 100, descent 120.

Observation UAVs are flown in a narrow range of lift coefficients. This can be seen from their wings: Like glider wings, they have a very high aspect ratio and a highly cambered airfoil. If you look at the optimum speeds for propeller and turbofan-powered aircraft, a high aspect ratio drives the optimum lift coefficient to high values which translates into a low calibrated air speed. Note that flying high does not necessarily mean that they operate at a low true air speed, however. Details depend on the altitude in which they are operated.
Let's look at the MQ-1 Predator for an example. Its aspect ratio is 19, and with all the protrusions I would guess the zero-lift drag coefficient to be no less than 0.025. This means the optimum lift coefficient for loiter is close to 2, which is probably above the maximum lift coefficient of the wing airfoil. For piston powered aircraft the best climb speed is identical to the optimum loiter speed, so the Predator should be flown close to its stall speed of 54 knots over the whole mission in order to get the most endurance out of this airframe. Note that the maximum g force the airframe can withstand is only 2, which means that top speed needs to be limited to 76.4 knots in order to avoid structural damage from flying into gusts.
Another giveaway is the low ground clearance of the tail surfaces: The predator lands at its regular flight attitude; there is no need to slow the aircraft down when it comes in for landing.
Short answer: The lift coefficient in all flight stages is high (0.8 to 1.4) while the true airspeed depends on the altitude. Turbofans tend to fly faster than piston-powered aircraft, but the difference is marginal.

Definitely a great answer, based on engineering judgment. I'd just add that most UAVs fly almost constant aoa (angle of attack) throughout the flight for maximum endurance. unless there's some urgency to speed up (high speed descent, escape weather, leave a scene, etc). During a mission their fuel mass changes considerably which in turn means slowing down gradually to fly the same aoa. touchdown technics may differ from vehicle to vehicle, but climb and approach both are dictated by the STANAG 4671 as 1.3 VS, unless another value is validated to be safe enough.


text:
Is there a way to calculate thrust without running experiments?
Is there any way to calculate the thrust generated without conducting experiments? In my case I need to figure out thrust generated by electric duct fans and/or turbojets.

A real world set up or some theoretical motor?

Yes, but you have to know more than is indicated in your question.

For the case of an electric motor driving a propeller, you can get a rough approximation for the thrust t from the power p consumed by the motor when the plane is flying with a constant velocity v, since $p = t \times v$. Of course, you should use coherent units, as newtons, m/s and watts, and include a large correction factor, as the real efficiency will be very far from 100%...
For the stationary case, in Wikipedia (entry 'disk loading') you can find an expression for the stationary case, derived from momentum considerations.

If you want to calculate the performance of a gas turbine engine, you can use a program like GasTurb. It will handle any gas turbine configuration, but it may not be able to calculate the thrust for your electric duct fan.


text:
What are the rules in UK law on carrying dangerous goods on drones?
If I wanted to use an unmanned drone for carrying potentially dangerous cargo like car fuel, what would be the legal requirements of this in the UK? For example, lets say I wanted to carry fuel in jerry cans for use by drivers who have run out of fuel.
What are the rules on commercial drone flights where the drone will be flying autonomously and out of visual sight of the operator?
What are the rules on carrying cargo like fuel in said drones?

I can't answer for UK. It's prohibited in the US under the new drone section para 107.36. I noticed it doesn't specify an exception if the drone runs on gas. I guess they figure any drone with a gas engine would be over the 55 lb limit.

@TomMcW My understanding of the legal term "carriage" is that it's for transporting goods or persons. If the drone is designed to run on a certain fuel, that's not carriage, but transporting a can of the same fuel is. I'm pretty sure LiPo batteries are also hazardous material, after all. That still makes this idea illegal in the US unless a waiver is obtained, though.

Would like to see how / if any of the dangerous goods regulatory bodies (ICAO, PHMSA) have issued any special permits for transporting dangerous goods via drones.

Article 94 of the Air Navigation Order

(1) A person must not cause or permit any article or animal (whether or not
  attached to a parachute) to be dropped from a small unmanned aircraft so as to
  endanger persons or property.
(2) The person in charge of a small unmanned aircraft may only fly the aircraft if
  reasonably satisfied that the flight can safely be made.
(3) The person in charge of a small unmanned aircraft must maintain direct,
  unaided visual contact with the aircraft sufficient to monitor its flight path in
  relation to other aircraft, persons, vehicles, vessels and structures for the
  purpose of avoiding collisions.
(4) The person in charge of a small unmanned aircraft which has a mass of more
  than 7kg excluding its fuel but including any articles or equipment installed in or
  attached to the aircraft at the commencement of its flight, must not fly the
  aircraft:
(a) in Class A, C, D or E airspace unless the permission of the appropriate air
  traffic control unit has been obtained;
(b) within an aerodrome traffic zone during the notified hours of watch of the
  air traffic control unit (if any) at that aerodrome unless the permission of
  any such air traffic control unit has been obtained;
  or
(c) at a height of more than 400 feet above the surface unless it is flying in
  airspace described in sub-paragraph (a) or (b) and in accordance with the
  requirements for that airspace.
(5) The person in charge of a small unmanned aircraft must not fly the aircraft for
  the purposes of commercial operations except in accordance with a permission granted by
  the CAA.

So section 3 states you must have direct visual contact and section 5 states that you must get permission from the CAA

An individual or organisation that would like to conduct regular flights with their drone, however, will probably need to submit an
    operating manual to the CAA for a permanent approval. This will allow
    greater freedom to operate continuously without the need to seek ad
    hoc approvals.

This type of Permission could be of use to:
emergency services a local authority that would like to use a drone to
  carry out maintenance inspections of its property As with a Permission
  to carry out a commercial operation, the CAA will need to be assured
  of the competence of the person who will be flying the device. The
  ‘pilot’ therefore will probably need to undergo an assessment process
  with one of the approved National Qualified Entities.

http://www.caa.co.uk/Commercial-industry/Aircraft/Unmanned-aircraft/Unmanned-Aircraft/

Note that even if permission were somehow granted to carry a can of petrol, the can and the UAV would need to be designed to ensure that the vapor would not be accidentally ignited.